Surface treatments used in daily manufacturing of parts for the automotive industry are selected to serve functional and decorative requirements achieved by mass production. Increased loads ...(mechanical, thermal, etc.), longer lifetime, weight reduction, friction reduction, and corrosion resistance are demanded for modern automotive systems. Within the last decade, improved and new deposition techniques were developed in PVD, PECVD, thermochemical heat treatment and thermal spraying. These new treatments are becoming more and more common in powertrain and engine applications. Generating optimized surfaces for different types of substrate materials (e.g. Al-alloys, case hardened steels, etc.) and geometries (e.g. bores) also impacts the running costs. Due to the new developments within these competing surface treatments, it becomes more and more common to substitute traditional treatment-substrate-systems with advanced treatments. Both the application potential and selected examples of different surface treatments will be shown. Aspects of the internal coating of bores inside the engine by plasma spraying, features of the corrosion protection of parts for the powertrain by the IONITOX process and piston ring treatments are discussed in more detail.
New advanced thermal spray technology allows providing wear-resistant coatings on the cylinder surface of aluminum or magnesium engines. The obtained special surface topography after the finishing ...allows to decrease significantly the coefficient of friction and to decrease the fuel consumption from 2% to 4%.
Engine tests on diesel and gasoline engines have confirmed the value of this technology regarding the aspect of energy saving.
This coating technology is introduced since 4 years in Europe by the manufacturing of high power diesel, respectively, gasoline engines. The combination of different MMC coating materials allows the development of new specific solutions for each types of engine. Coatings with improved corrosion resistance and abrasion resistance were also developed and are available now. A brief overview on other applications of thermal spraying in the automotive industry will be given also.
The fluctuating behavior of a Sulzer Metco F4 DC plasma gun has been investigated by simultaneous measurement of the time dependencies of the are voltage and of images from the nozzle interior. An ...end-on imaging arrangement using a mirror and a mask in the optical path from the are to the camera allows visualization of the anodic arc attachment by strongly attenuating the bright emission from the are column. With the torch operating in the restrike mode, sequences of images have been acquired in synchronization with several typical features of the are voltage fluctuations showing that the attachment nature changes during a restrike cycle. Multiple attachments which coexist at least during the 1 /spl mu/s exposure time of the camera have been evidenced and are interpreted as a continuous process of creation/vanishing of successive arc roots with a smooth transfer of the current from one to the other. The anode wear is shown to have a strong effect on the root position over the anode periphery, with a preference for attachment in eroded regions. The effects of operation parameters such as current, gas flow and injector type on the attachment nature and position are also presented.
The aim of this study was to determine to what degree polymerase chain reaction (PCR) was superior to histology and culture, and whether a noncommercial urease test was of value, in detecting
...Helicobacter pylori in gastric biopsy specimens. Gastric biopsy specimens from the antrum and corpus of 134 consenting patients were subjected to PCR, targeting the
glmM (
ureC) gene, histology, culture, and a rapid urease test. PCR detected
H. pylori in the biopsy specimens from 59 patients. All methods showed a high degree of sensitivity and specificity, but histology gave 2 false-negatives, and culture and the urease test gave 1 false-negative compared with PCR. PCR of a
glmM gene segment was superior to the other methods for the detection of
H. pylori infection and was comparable to histology in terms of cost. Nevertheless, in this study, histology and culture were found to be relatively reliable methods for examining gastric biopsy specimens.
Background
: Better control of gastric acid secretion with omeprazole appeared to decrease the need for dilatation of oesophageal strictures complicating gastro‐oesophageal reflux disease in our ...hospital‐based endoscopy service.
Aim
: To investigate whether the perceived decrease in the need for oesophageal dilatation could be documented from endoscopy records, and, if confirmed, whether this could be related to the treatment used.
Patients and methods
: Retrospective study of the records of 69 patients who had peptic oesophageal strictures dilated, followed by treatment with acid inhibition for at least 6 months. Mean duration of follow‐up was 3.9 years during treatment with H2‐receptor antagonists and 2.1 years while on omeprazole (258 and 78 patient‐years, respectively). Re‐dilatation rates were compared between those treated with H2‐receptor antagonists or omeprazole.
Results
: There has been a significant decrease in dilatations performed for gastro‐oesophageal reflux induced strictures (P < 0.001), while dilatation rates for other indications remained constant. Treatment with omeprazole not only decreased the need for further dilatations, but also prolonged the mean time between any further dilatations to 26.3 months compared to 9.3 months for those on an H2‐receptor antagonist (P < 0.0001).
Conclusions
: Following dilatation of peptic oesophageal strictures, treatment with omeprazole in place of an H2‐blocker significantly decreases the need for repeat dilatation.
Background: ERCP is increasingly performed not only in large referral centers but also in smaller units. We sought to analyze the success rates of selective cannulation and intervention using the ...cumulative sum method and to document the workload in a small unit.
Methods: Indications, results, and interventions performed by one endoscopist were recorded for all patients undergoing ERCP at Dunedin Hospital. Selective cannulation and successful intervention were used as outcome measures and, using the cumulative sum method, compared to a target value of 90%.
Results: Over an 8-year period, 532 ERCPs were performed. Overall 91% and 81% of selective cannulation and interventions respectively, were successful. The cumulative sum method plot shows that satisfactory outcomes for selective cannulation were obtained after some 100 to 120 procedures and after some 120 interventions. ERCP was normal in 171 (32%) patients, stones were found in 169 (32%), and strictures in 81 (15%) patients.
Conclusions: The cumulative sum method is a valuable tool to compare individual performance with a nominated target value and to ensure that an acceptable outcome is achieved and maintained. These results show that small units can develop and maintain expertise in ERCP if procedures are performed regularly.(Gastrointest Endosc 1997;46:48-52)
The rolling contact fatigue (RCF) behaviour of thermally sprayed WC-Co coatings with nominal compositions of WC-12%Co, WC-10%Co-4%Cr and WC-17%Co was studied with a two-roll configuration ...roll-against-roll testing apparatus under 420–600 MPa Hertzian contact stresses in unlubricated pure rolling conditions. The coatings were prepared by atmospheric plasma spray (APS) and two high-velocity oxyfuel (HVOF) spray processes. In the APS sprayed WC-12%Co coating the RCF damage was dominated by an increased surface roughness due to spallation of flakes and a formation of a network of cracks within the coating layer. HVOF sprayed WC-12%Co and WC-10%Co-4%Cr coatings were damaged either by the formation of vertical, linear cracks or pitting of the contact surface. The formation of pits in the HVOF sprayed coatings was significantly less than that found in the APS sprayed coatings. The HVOF sprayed WC-17%Co coating showed the best RCF behaviour among the studied coatings with unchanged surface roughness, no formation of cracks and only a few pits were found on the contact surface. The good resistance of this coating against formation of failure in the RCF testing is caused by its higher ductility and fracture toughness due to a higher metallic binder content in comparison with the other coatings. Other characteristics such as a low amount of brittle Co-W-C carbides and a dense microstructure are also believed to be beneficial for a RCF resistant coating.
Surface preparation of substrates is a major stage in thermal spraying as it greatly influences coating adhesion. Standard grit-blasting creates roughness but also often leaves grit inclusions at the ...substrate surface, which are detrimental for coating quality. In contrast, the use of smooth substrates involves improvements in metallurgical adhesion.This work deals with the use of substrate pre-heating and of the PROTAL® process (‘PROjection Thermique Assistée par Laser’) to promote metallurgical adhesion. PROTAL is based on substrate laser treatment prior to spraying to achieve an oxide-free interface and, under specific conditions, which modifies the substrate morphology. A metallurgically reactive system (i.e., copper sprayed onto Al 2017) was selected to be suitable for controlling metallurgical features at the coating-substrate interface (mainly pores, intermetallic phases and pre-existing cracks). These were shown to depend on substrate roughness and on the substrate temperature during the first spraying pass.LAser shock adhesion test, namely LASAT, was developed to enable morphological and metallurgical features of as-sprayed interfaces to be studied separately. The existence of a critical roughness for anchoring (CRA) and of an adhesion transition temperature (ATT) could be assumed. As for metallurgical properties, interface intermetallics and pre-existing cracks were shown to be detrimental for adhesion. Moreover, LASATesting succeeded in showing that adhesion of PROTAL coatings is better than that of APS-only coatings.
Thermal spray techniques can fulfill numerous industrial applications. Coatings are thus applied to resist wear and corrosion or to modify the surface characteristics of the substrate (e.g., thermal ...conductivity/thermal insulation). However, many of these applications remain inhibited by some deposit characteristics, such as a limited coating adhesion or pores or by industrial costs because several nonsynchronized and sequential steps (that is, degreasing, sand blasting, and spraying) are needed to manufacture a deposit. The PROTAL process was designed to reduce the aforementioned difficulties by implementing simultaneously a Q-switched laser and a thermal spray torch. The laser irradiation is primarily aimed to eliminate the contamination films and oxide layers, to generate a surface state enhancing the deposit adhesion, and to limit the contamination of the deposited layers by condensed vapors. From PROTAL arises the possibility to reduce, indeed suppress, the preliminary steps of degreasing and grit blasting. In this study, the benefits of the PROTAL process were investigated, comparing adhesion of different atmospheric plasma spray coatings (e.g., metallic and ceramic coatings) on an aluminum-base substrate. Substrates were coated rough from the machine shop, for example, manipulated barehanded and without any prior surface preparation. Results obtained this way were compared with those obtained using a classical procedure; that is, degreasing and grit blasting prior to the coating deposition.
PDF
