This week, the ratings of four chemicals stocks on Portfolio Grader are down. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

A. Schulman, Inc.’s (SHLM) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. A. Schulman sells plastic resins and compounds, which are used as raw materials by its customers. The stock price has dropped 6.7% over the past month, worse than the 1.3% decrease the Nasdaq has seen over the same period of time. The stock’s trailing PE Ratio is 32.60. To get an in-depth look at SHLM, get Portfolio Grader’s complete analysis of SHLM stock.

This week, Airgas, Inc. (ARG) drops from a C to a D rating. Airgas is a distributor of industrial, medical, and specialty gases and hardgoods, such as welding equipment and supplies. For a full analysis of ARG stock, visit Portfolio Grader.

OM Group, Inc. (OMG) earns a D this week, falling from last week’s grade of C. OM is a global solutions provider of specialty chemicals, advanced materials, and technologies. The stock gets F’s in Cash Flow, Margin Growth and Sales Growth. For more information, get Portfolio Grader’s complete analysis of OMG stock.

Hawkins, Inc. (HWKN) earns an F (“strong sell”) this week, moving down from last week’s grade of D (“sell”). Hawkins formulates, manufactures, blends, distributes, and sells reagent grade laboratory chemicals and industrial chemicals. To get an in-depth look at HWKN, get Portfolio Grader’s complete analysis of HWKN stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.