Technology Interchange—Factors to Consider When Calculating Line Speed

By Jeff Behymer

In our line of work, we partner with OEM equipment manufacturers and job shop coaters across the country. The diversity of industries creates a wide variety of coating needs. End user parts range in size and complexity and so do the related coating processes. These processes include material handling, masking, pretreatment, coating, and curing of parts.

It is ideal when the OEM end user already has an internal specification (or spec sheet) for coating their parts. This allows them to maintain the quality of their finishing process internally or effectively communicate the requirements to a third party or job shop coater. Racking systems or load bar configurations used internally can also be shared with the job shop coater as this allows them to job cost more accurately. The reality is that many OEM end users do not already have this available, and their products potentially suffer or the burden shifts to the job shop coater.

When designing a new engineered finishing system, we discuss the key components required for the customer at plant level (or by location for companies with multiple sites). We start with goals, required features, space requirements, and throughput. We then follow that up with discussions related to budget and timeline. While everyone wants the best product for the best price as quickly as possible, the reality is we need to identify the right solution that will meet the end user goals and it will take some time to get it right.

Basic Building Blocks
A major key to successfully implementing the right solution is to take the complexity of each end user need and funnel it through the same process using basic building blocks. What may seem complex at the time can be simplified by using this method for each new system.

Using the same process repeatedly produces calculations that can be trusted because they are tried and true. However, there are instances where end users will request a real-world or simulated trial using their own or similar parts. Real-world trials typically take place on existing systems located near the end user, while simulated trials take place at the integrator’s facility. Once a trial or trials are complete, most (if not all) questions related to how the system will meet their needs will have been answered.

For the purposes of this column, we will focus on the basic building blocks related to integrating a powered conveyor into a system and calculating the line speed. Line speed can be based on several factors. The first and generally most important factor is throughput. At this point, there are many questions that will need to be answered. See the examples below:

1. How many production hours are in a shift?
2. How many parts does the end user want to produce in one, two, or three shifts?
3. Will the laborers loading and unloading the line be able to keep up at an “x” feet per minute line speed(s)?
4. Can parts be manufactured in groups or families to increase line density?
5. The last question is a building block for maximizing line density. Using a plan for hanging parts will have an impact. For example, groups or families of parts can often be hung more efficiently, or even offline, using racking systems. This helps maximize the space on a line and presents a consistent transfer efficient. How parts are hung will also have an impact on the line speed. We recommend taking all factors into account when setting the line speed as we do not recommend regularly making changes due to the negative impacts that could create.

Being Calculated
Calculating line speed also establishes the footprint for each system component and the overall space that will be required in the facility to take powder ‘from the box to the part.’

There are several factors at play when calculating line speed.

1. Understand the desired throughput, whether it be daily, monthly, or annually.
2. Use the technical data sheets (TDS) from the material supplier(s) to understand the characteristics of the coating.
3. Consider part data. The heavier the part, the longer it will take for it to reach temperature in the cure oven.
4. Know the maximum weight of the part(s) to select the appropriate style of conveyor.
5. Determine the maximum part (or group of parts) dimensions to create a work envelope (or box) that will travel through each component of the system.
6. Use a turn study to make sure you have proper clearances for the inside dimensions of your equipment or support columns for the conveyor itself.
7. Determine line density based on load/unload capabilities.

Once we have this basic information, we have a solid idea of what will be needed. Our primary goal is to determine how much conveyor length will be needed in the oven. We then take the dwell time for the part in the oven and multiply it by the desired line speed (all factors considered). For example, if 30 minutes of dwell time is required and the system is running at 6 feet per minute (FPM), then 180 feet of conveyor will be required in the oven. The actual designed layout will be based on available space in the facility.

One thing to point out is that an OEM who coats their own parts on a daily basis will have a clearly defined work envelope or cubic box (L x W x H) for their max part or group of parts. This makes it easier to define the work opening for each component of the finishing system while also using turn studies to ensure proper clearances. The OEM will also have a relatively accurate production forecast which helps determine the desired throughput by shift.

For the Job Shop Coater
How does this differ for a job shop coater? The answer is our process remains mostly the same. We generally build a system for an OEM or job shop coater using the 80/20 rule. Design it to coat the majority, or 80%, of parts without being distracted by low runners or other variables that are counterproductive.

In this instance, a job shop coater will identify the optimal work envelope based on factors such as opportunities in the area or companies that have identified them as a potential supplier. The only variable for the job shop coater is they will not have clearly defined annual production volumes or forecasts like an OEM manufacturer. They will instead look at the dollar value associated with each linear foot of their system and fill it up based on capabilities that will be organic in nature. We recommend they find an optimal line speed and set it based on their current or projected workload, taking material data (primarily cure cycle) into consideration. Line speed for the job shop coater will typically be used to calculate the cost of a job and price it accurately to their customers.

Understanding these basics will help many end users maintain or create a coating specification that can be supplied to any of the suppliers involved in the process of coating their parts.

Jeff Behymer is managing partner at Spray Tech Industrial Solutions.