Base material selection preparation and prior processes.
Yes you can. For a suitable tool steel, the TD Coating process will harden the tool and tempering after hardening is also performed.
However, it is important to note that there will be more chance of material movement when coating an unhardened tool as compared to a pre-hardened tool. For tighter tollerances we recommend vacuum hardening , grinding to size and then coating. Call us to discuss this option.
Yes, provided it has been gas or plasma nitrided. A nitrogen rich layer on the surface of the steel means that a comination fo Vanadium Nirides and Vanadium Carbides are formed. Vanadium Nitrides are also hard and well bonded , but may perform differently to pure Vanadium Carbide in certain applications.
If the tool has been liquid nitrided, then in many cases this leads to a spoiling of the coating. Even when the surface is polished to a mirror finish after salt bath nitiriding, a rough TD layer is formed which is not suitable for heavy duty use.
To remove a nitrided layer, the item must either be ground, anealed or vacuum re-hardened to physically remove the layer or thermally break down and disipate the nitrided layer.
Surface finish plays an integral part to the performance of most coated tool applications. The higher the surface load in general , the better the surface finish should be. The TD coating is too thin to “fill” or cover scratches, grinding lines, machining lines or galling damage. Thus the surface you have before coating represents the surface you will recieve after coating.
Also, don’t forget that due to the extreme hardness of the coating, a micro-rough surface coated with TD, may act more like a file, than a slippery aid to a forming process for example.
TD is essentially a chemical reaction between active free carbon that becomes available in the steel and surplus Vandium ions supplied in the salt bath. The carbon available in the matrix is based on a) carbon content and b) treatment temperature. So basically for a steel to be coatable with TD the steel must contain at least 0.3% C and should in most cases have an austenising/hardening temperature of approximately 950 °C. If the carbon content is too low then coating may not form and if the processing temperature is too low, the coating process may not be efficient. If we were to coat a tool at 1030°C when its maximum austenizing tempereature is only 870°C , this would completely damage the microstructure of the tool. Also water quench and oil quenching steels are generally avoided for TD and Salt and air hardening steels are preferred.
Refer to this table for commonly coated tool steels. If you have a particular query for a steel not listed, please contact us for direct advice.
The TD process is performed as part of a heat treatment cycle and justÂÂ like you need to specify which steel you have submitted to a heat treater, we need to know too. This enables us toÂÂ establish times, temperatures and suitabilities for TD coating. TD is also a chemically based process and as suchÂÂ the chemistry and any other processes that may have been previously performed need to be reported to ensure we are still able to process the tool. The PDS also indicates information such as critical tolerances that need to be maintained and working ares , sharp edges and any other important information that ensures that we get the job rightÂÂ first time, and this also gives us the best chance of addressing problems before we start. The PDS is the first step to detailing the job card and with this information supplier the job can experience the least ammount of delay before approval for processing.
The TD process is performed as part of a heat treatment cycle and justÂÂ like you need to specify which steel you have submitted to a heat treater, we need to know too. This enables us toÂÂ establish times, temperatures and suitabilities for TD coating. TD is also a chemically based process and as suchÂÂ the chemistry and any other processes that may have been previously performed need to be reported to ensure we are still able to process the tool. The PDS also indicates information such as critical tolerances that need to be maintained and working ares , sharp edges and any other important information that ensures that we get the job rightÂÂ first time, and this also gives us the best chance of addressing problems before we start. The PDS is the first step to detailing the job card and with this information supplier the job can experience the least ammount of delay before approval for processing.
It is not a strict requirement to have parts vacuum hardened if they are to be TD coated, but this is highly recommended. Vacuum offers the cleanest hardening technology with the lowest chance of surface contamination/chemical change during hardening. Neutral salt bath hardening on occasion is not always that neutral and can either diffuse other elements into the surface of the steel or alternatively diffuse carbon out of the steel, both of which can affect the TD coating chemistry adversely. Hardening from a case hardedning/carburising salt bath or cyanide bath must be strictly avoided before TD as this leads to spoiled coating. Please advise us if this is the case as a pre-treatment may be necessary.
TD Process Questions
Yes. Items that do not have strict dimensional requirements can be recoated mutiple times. It is usual to strip the coating and repolish the base material to remove damage to the exposed base material. If there has been no damage to the base material, blending is sometimes possible.
If you wish to grind the coating off a certain area, as in a bearing journal for example, yes this is possible. Due to the hardness of the coating, the grinding wheel may skid and battle to spark, but eventually the grinding wheel will penetrate the coating. We would suggest leaving approximately 0.15-0.2 mm of stock material per side for grinding.
If however, you wish to adjust the final size by grinding the coating, as is done after chrome plating, then this is not possible.
In most cases, the answer is no as applications are generally looking for greater than 0.03mm. Build up coatings usually require grinding back to size of the coating and this is not possible with TD as the layer is too hard and too thin.
Also if your application only requires a few microns of build up, it may be that the base material size movement may be more influencial to the final size than the coating thickness.
TD is better suited to being a preventative wear coating than a repair coating.
No, the coating itself neither increases nor decreases the toughness of the tool. However, since the TD process involves heat treatment , this can change the condition of the underlying tool steel.
Please advise TDCCI on your PDS if you have an application that is maximum toughness critical or has suffered from prior breakage or cracking so we can advise on optimum material selection and/or pre, during and post TD heat treatment specifications for your application.
Shape distortion is dependant on your parts geometry. Long slender items , as well as thin walled cylinders are most prone to shape distortion. We will advise if we feel a part is too risky for processing based on its geometry.
Size distortion is due to change in volume of the steel during thermal processing. Most customers are familiar with the change seen when hardening a tool after machining. Steel can grow or shrink considerably. Since most steels TD processed are already hardened and tempered , there is less change when returning to this hardened and tempered condition. Thus size change is mostly far less than that experienced during first time hardening.
Also , size change is percentage based and thus the greater the Dimension the greater the resultant growth or shrinkage can be. This can be as much 0.1% but is generally far less when following know heat treatment. Some manipulation of sizes is possible to adjust sizes , but this is not always predicatable.
Please inform us on your PDS if you have a tight dimensional tollerance requirement.
Post Hardening is also called Vacuum Re-hardening. This is performed mostly on high weight parts as well as certain applications where the base hardness of the tool steel under the coating is critical to the part performance. Straight from the TD process, the maximum hardness from the tool steel may not be achieved due to a slower quench rate through the td process. PH can restore the few lost HRc points that make the difference between the coating performing 100 000 components and 150 000.
The Vacuum protects the coating from re-oxidising at harndening temperatures.
The max part dimensions are approximately 450 mm diameter by a height of 600 mm. If you have a part very slightly larger than this , this may be possible but will need to be discussed with the process engineer.
Timing cost and payment
TD Coating is most generally priced on the weight of the tool steel coated, however there are other factors that influence the cost. Some of these are physical size, quantity and frequency, jigging efficiency, special material types.
Other factors that influence the total cost of a coating job are pre-polishing and vacuum post hardening if these necessary.
TD -There are many process steps to complete in order to complete aÂÂ TD job. If the job is received at the bgining of the week with a completed PDS, this should be dispatched within the same week.ÂÂ Turnaround time also depends on quantity,ÂÂ TDCC workload and scheduling. Please make sure you communicate with TDCC should you have urgent time requirements so we can answer to your specific situation. A general guideline is, theÂÂ fastest delivery is 3 days, average of 5 days and longest is 7 days.ÂÂ
PVD-usually 5 working days. TiN loads run more frequently than TiAlN loads. For very large items and where pre-polishing is required, please extend delivery estimate.
Armoloy- usually 4-5 working days
Other Coatings -Please enquire
Payment Terms are COD for all new customers. For frequent repeat customers that complete credit application forms and are have a good credit history, a 30 day account can be opened. We prefer electronic transfer and cheque over cash.